Retinal neovascularization or growth of new blood vessels from pre-existing retinal vessels is the leading cause of blindness in the United States among working-age adults (diabetic retinopathy) and infants (retinopathy of prematurity). It is well accepted that hypoxia is the initial stimulus for neovascularization or angiogenesis in the retina in these conditions. The final, pathway in the angiogenic process is the invasion of extracellular matrix and migration of microvascular endothelial cells. This phase is dependent upon the expression of a variety of extracellular proteinases including the serine proteinase urokinase and members of the matrix metalloproteinase (MMP) family. This proposal will test the following hypothesis: retinal neovascularization is facilitated by the hypoxia-induced expression of extracellular proteinases by retinal microvascular endothelial cells. The broad, long-term goals of this study are to examine the role of these proteinases in retinal angiogenesis, and to test the efficacy of antagonists to these proteinases in inhibition of new vessel formation. Specific aims of the proposal are: (1) To characterize the expression of proteinases and inhibitors during the active stages of angiogenesis by using biochemical, histological, and molecular biological techniques. The spatial and temporal expression of these proteinases and their inhibitors will be studied in the well- characterized mouse model of retinal neovascularization. The role of different cell types in the retina in this process will be determined by immunohistochemical and in situ hybridization techniques. (2) To determine whether isolated retinal capillary endothelial cells can respond independently to hypoxia with a change in their proteinase/inhibitor profile. This will be studied by exposing cultured retina endothelial cells to hypoxia and/or vascular endothelial growth factor (VEGF). Also, it will be examined whether hypoxia plays any role in protein expression through the production and/or activation of hypoxia inducible factor (HIF- 1 alpha). (3) To determine if the process of retinal neovascularization can be inhibited through the use of specific proteinase inhibitors in the mouse model.